Comic Relief chief Kevin Cahill. ‘With the barrage of events this year it's easier to donate without even thinking about it.' Photograph: Graham Turner for the Guardian

At risk of being thought a jerk, I won't be giving to Comic Relief this year. Confession time: I haven't given to Comic Relief any year in the past either, preferring instead to donate and fund raise for smaller and local charities. But with the barrage of ads, social media pushes and events this year, it's become easier to donate without even thinking about it.

So I almost did – sending a text to donate – when it occurred to me I had no idea what Comic Relief was raising money for. Everyone knows why it started: in 1985, with famine in Ethiopia one of the world's biggest stories, the campaign was launched. Since then, it's grown massively and embraced a wide variety of charities and causes. Some of which, as it happens, you might be reluctant to support.

With hundreds of projects being funded it's difficult to pinpoint exactly where the money goes. But we can make an educated guess from the information given on the website. Under "Sexually Exploited and Trafficked Young People", for instance, we are informed of several frightening things intended to loosen your pocket change, like "75% of women working in prostitution started before they were 18".

Uh-oh, dodgy stats klaxon! This figure comes from a paper that surveyed only street-based sex workers, who represent less than 20% of prostitution in the UK. It also states: "Our research indicates that the majority of women who contact their clients on the streets are considerably younger than the women who work in other forms of prostitution." It's typically used by groups who target sex workers as well as trafficking victims.

Does this mean we shouldn't be concerned about the age at which street sex workers enter prostitution? Of course not. Rather, we should be careful about – and wary of – any group that throws around this number as if it represents sex work in general. It's these kinds of generalisations that often indicate a broad-brush and potentially damaging approach to addressing people's needs.

Similarly, we are regularly told that the "average" age of entry into sex work is 13. This is actually incredibly mathematically unlikely, unless there is an epidemic of infants being sexually exploited we don't yet know about. Former librarian and escort Maggie McNeill has broken down why this oft-repeated assumption is incorrect. Emi Koyama has done the same, pointing out that the most commonly cited source for the average age of entering prostitution was a badly designed study that only surveyed people aged 18 or under, so by definition did not include anyone who entered at an older age.

For comparison, I became a call girl at the age of 27. For every one of me, to arrive at an average of 13, you'd need someone aged minus one. Or five 10 year-olds. Or ten 12 year-olds. You get the picture. Not impossible, but not apparently happening in the UK and very unlikely to be going under the radar if it was, despite the protestations of what anthropologist Laura Agustin calls the rescue industry. The Comic Relief site continues: "The UK is a major destination country for trafficked young people. They are at a very high risk of being sexually exploited."

No source is given for this statement – probably because no such data exists. Confirmed trafficking cases in the UK are more likely to enter other jobs like agriculture, hospitality, and domestic service than they are to become sex workers. Forced labour of any kind is a concern, more so when young people are involved. Which is why getting trafficking efforts right matters.

Unfortunately it has often been the case that anti-trafficking causes bleed over into anti-sex work ones, confusing forced labour with choice, and putting the people involved in sex work at greater risk of harm. Regardless about how one feels about paid sex between consenting adults, the safety of those involved must come first. Too often, anti-trafficking measures have been shown to harm rather than help.

While I don't expect that the problems of teasing out the victims of forced labour from the genuine workers is top of everyone's list of concerns, it is worth remembering that the bigger the charity, the more likely money is to go somewhere you weren't expecting. Just ask donors to Bono's ONE Campaign, many of whom did not realise the group's thrust was awareness-raising for hunger and health causes, that is, glossy events and big media campaigns rather than on-the-ground help [see footnote].

I have no doubt that many of the charities and causes supported by Comic Relief are worthy recipients who use the money well. So why not cut out the middle man and donate directly instead? The difference between charity and tax is having a say in where the money goes: an enormous national clearing house of "good causes" isn't going to do that. In an economic climate where charities are struggling to raise the funding they once did, we owe it to the causes we support to make sure as much money gets into their hands as possible.

• ONE has asked us to point out that it does not raise funds from the general public and does not run on-the-ground programmes. It says it is not correct that any donors have not realised that its main purpose is advocacy and campaign work, as is made clear on its website.